Winter Surface Temperature Anomalies in Japan and East Asian Atmospheric Circulation Patterns Associated with ENSO Kiyoharu Takano, Chiaki Kobayashi Meteorological Research Institute /JMA Shuhei Maeda,Shoji Kusunoki Japan Meteorological Agency

Objective To clarify the mechanism that brings warm winter in Japan during ENSO warm episode (Halpert and Ropelewski, 1992). Winter(DJF) Surface Temperature Tendency in Japan during Warm Episode of ENSO

Northern Japan Western Japan The Nansei Islands Eastern Japan

Early Winter 3month mean (October, November, December) Late Winter 3-month mean (January, February, March Tmp850 correlation map with NINO3 SST ( ) 39years

Division of Winter into Early Winter and Late Winter Early Winter October-December (Influence is over whole of Japan) Late Winter January-March (Influence is only southern part of Japan)

Data and Analysis Procedure Data : NCEP/NCAR Reanalysis 1979(59)-1993 CMAP (Seasonal Predictability experiment with Prescribed SSTs) Analysis: Correlation and Regression map from NINO3 SSTs Vorticity analysis at 200hpa

Regression map with NINO3 SST (Late Winter JFM) Precipitation Temperature at 850hPa Stream function at 850hPa Stream function at 200hPa

Western tropical Pacific pattern ・ Negative precipitation anomalies ・ Anti-cyclonic pattern at lower level ・ Cyclonic pattern at upper level Matsuno-Gill Response to relative cooling (Bin Wang et al. 2000)

Late Winter(JFM) Temperature Advection by Lower Circulation (Bin Wang et al. 2000, Yasutomi and Kimoto 1999) Direct Effect : Influence is restricted in Southern Japan Temperature at 850hPa Stream function at 850hPa

Temperature at 850hPa (JFM) Advection by anomaly wind (JFM)

Regression map with NINO3 SST (OND) Precipitation Temperature at 850hPa Stream function at 850hPa Stream function at 200hPa

Early Winter(OND) Warm surface temperature is brought by barotropic circulation near Japan which propagates from southern China. Stream function at 200hPa and Takaya-Nakamura(TN) Wave activity flux (TN Flux shows Rossby wave propagation and activity G.R.L. 1998)

Warm(Cold) winter in Japan during warm(cold) episode of ENSO is brought by (a)Late winter(JFM) Temperature advection by low level circulation over Western Pacific This is direct influence of ENSO and the influence is restricted in the southern Japan. (b) Early winter(OND) Barotoropic (positive) circulation which propagate from southern China. This is indirect influence of ENSO and influence is over whole of Japan. Both effects originally come from negative(positive) precipitation anomalies in the Western tropical pacific during warm(cold) episode.

Discussion Why the mechanisms in JFM and OND are different ? = Why Rossby wave propagates from southern China to Japan only in OND and not in JFM? (a) Difference of Precipitation anomalies in the tropical western Pacific? Not so different ? (b) Difference of basic flow? Not so different ? (c) Other reason? Stream function at 200 and TN flux JFMOND

A Possibility Zonal component has large amplitude in JFM （ Tropical Axisymmetric Mode (Watanabe et al.2002)) Stream function at 200hPa OND Zonal mean component Ratio of zonal mean component to total amplitude JFM OND Stream function at 200hPa JFM Zonal component of forcing is stronger in JFM than in OND.

Vorticity equation liniarized around the climatorogical basic state at 200 hPa L: Liner operater ψ c ： Basic State(climatology) ψ d : perturbation F d : Perturbation forcing It can be solved symbolically,

Note has non-zonal component, because basic state ψ c has non-zonal component. We consider to divide forcing into zonal component and non-zonal component.

Liner solution by non-zonal forcing Liner solution by zonal forcing Liner model by total forcing Regression from NINO3 SSTs Late Winter (JFM) case Liner response by liner barotropic model

Wave activity flux for response to total forcing Wave activity flux for response to non- zonal forcing

Liner model by Non zonal forcing Liner model by zonal forcing Liner model by total forcing Regression from NINO3 SSTs Early Winter (OND) case Liner response by liner barotropic model

Hypothesis There is Rossby wave propagation from southern China to Japan both in early and late winter as a response to local (or non-zonal) forcing. However, in late winter, since zonal forcing is stronger, non-zonal response to zonal forcing covers this Rossby wave propagation, and then it can not be seen. On the other hand, in early winter since zonal forcing is weak, Rossby wave propagation can be seen.

Conclusions A.Warm winter in Japan during warm episode of ENSO is brought by different two mechanisms depend on the period. (1) In early winter(OND), barotropic Rossby wave propagating from southern China. (2) In late winter(JFM), temperature advection by lower level anti-cyclones flow in the tropical western Pacific. B. The difference of these two mechanisms may be understood by considering the effect of non-zonal response to zonal forcing which is stronger in late winter.